A problem of drain of resources typified by oil has become realistic, and thus government policy and many measures have been taken for environment protection. On the other hand, on an individual level, more and more people are conscious of environment protection, and more and more eco-friendly products are available in markets. New fields which we can call environment protection market or environment protection business have been established.
Nevertheless, consumers tend not to accept low quality of life caused by eco-friendly products, and thus it is necessary for manufacturers to manufacture products that can guarantee high quality of life as well as achieve resource saving, which must lead to increase in business competitiveness. Note that the term “resource saving” has two meanings. One is resource saving in manufacture of products or in consumption cycle of products, which is achieved by eliminating wastes of materials or increasing duration period of products. The other is the reduction of energy consumed in use of products, which is realized by improvement of fuel-efficiency and reduction of power consumption.
Organic EL televisions are widely known as the next generation displays after plasma televisions and liquid crystal televisions. Organic EL televisions use, as pixels, light-emitting elements in which a layer including an organic compound is interposed between electrodes and which emit light by supply of current to the light-emitting elements. Thus, organic EL televisions do not need backlights, which enables the production of extremely flat displays. Further, organic EL televisions have excellent visibility and high response speed. In addition, because organic EL televisions can readily display images with high contrast ratio, they are promising, next generation displays that can exhibit high quality images.
On the other hand, currently commercial organic EL televisions consume electric power about 1.5 times as much as liquid crystal televisions having the same size. It is considered that organic EL televisions can potentially realize lower power consumption than liquid crystal display televisions. However, currently available organic EL televisions still do not possess such a product level.
In recent years resource saving and energy saving are demanded. If organic EL televisions can realize their potential thoroughly and surpass the liquid crystal televisions in power consumption, the organic EL televisions must be an extremely attractive product that is capable of gratifying users' motivation for environment protection and improving quality of life.
There are a wide variety of approaches to reduce power consumption. As for display devices using self-luminous light-emitting elements in pixels, e.g., organic EL televisions, emission efficiency of such light-emitting elements is increased and thereby power consumption can be reduced. Therefore, a large number of studies regarding improvement of emission efficiency of light-emitting elements have been made (Reference 1: Japanese Patent Application Publication No. 2007-227117).